This application claims benefit of Korean Application No. 2002-35674 filed Jun. 25, 2002 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an apparatus for driving developers of a color image forming apparatus, and more particularly, to an apparatus for sequentially driving a plurality of developers separated a predetermined distance from a photosensitive body in a color image forming apparatus.
2. Description of the Related Art
In general, an electrophotographic printer such as a color laser printer includes an image forming apparatus which forms an electrostatic latent image on a photosensitive body and develops the electrostatic latent image with toner. Then, the developed image is transferred to paper by a predetermined transfer medium and is pressed and heated to completely fix the image on the paper.
FIG. 1 shows an example of an image forming apparatus of a color printer. Referring to FIG. 1, an image forming apparatus includes a photoreceptive drum 10 which is a photosensitive body, a charger 11 which charges the photosensitive drum 10, a laser scanning unit (LSU) 12 as an exposing unit which forms an electrostatic latent image by scanning light onto the charged photoreceptive drum 10, a development unit 13 which develops the electrostatic latent image with four colors of black (K), yellow (Y), magenta (M), and cyan (C), a transfer belt 14 on which four different color images developed on the photoreceptive drum 10 are sequentially overlapped, a first transfer roller 14a which transfers the image developed on the photoreceptive drum 10 to the transfer belt 14, a second transfer roller 14b which transfers the image of four overlapping colors on the transfer belt 14 to paper, and a fusing unit 15 which presses and heats the paper to fix the transferred image on the paper. Developing rollers 13a-K, 13a-Y, 13a-M, and 13a-C of four developers 13-K, 13-Y, 13-M, and 13-C provided in the development unit 13 are arranged separated by a predetermined gap from the photoreceptive drum 10 and sequentially develop the electrostatic latent image on the photoreceptive drum 10 when a development bias voltage is applied to corresponding developing rollers. Reference numerals 16, 17, 18, and 19 denote a paper cassette for storing a supply of paper, a blade for cleaning the photoreceptive drum 10, an eraser, and a transfer path along which the paper is ejected, respectively.
The image forming apparatus having the above structure performs an image forming process as follows. First, when the charger 11 charges the photoreceptive drum 10, the LSU 12 scans light to form an electrostatic latent image of an image to be developed with the first color. For example, when black is to be developed first, a predetermined bias voltage is applied to the black developing roller 13a-K. Then, a development unit driving motor (not shown) drives the developing roller 13a-K so that a toner adhering on the outer circumferential surface thereof is transferred to a portion of the photoreceptive drum 10 contacting the developing roller 13a-K. The black image developed as above is transferred to the transfer belt 14 via a first transfer nip N1. Next, an electrostatic latent image for the second color is formed through the charging and exposing steps with respect to the photoreceptive drum 10. For example, where yellow is to be developed secondly, a predetermined development bias voltage is applied to the yellow developing roller 13a-Y and the developing roller 13a-Y is driven to develop the electrostatic latent image on the photoreceptive drum 10. The yellow developed as above is transferred onto the transfer belt 14 to overlap the black image previously transferred to the belt 14. In the same manner, images of the third color, magenta, and the fourth color, cyan, are developed and transferred so that an image having a desired color is completely formed on the transfer belt 14. Thereafter, the completed color image formed on the transfer belt 14 is transferred to paper supplied to a second transfer nip N2 between the transfer belt 14 and the second transfer roller 14b. As the paper passes through the fusing unit 15, the color image is heated and pressed to be completely fixed onto the paper.
FIG. 2 is a view showing a structure of a driving apparatus of the development unit of FIG. 1. FIG. 3 is a partial plan view of the driving apparatus of FIG. 2.
Referring to FIGS. 1-3, the developing rollers 13a-K, 13a-Y, 13a-M, and 13a-C are arranged around the photoreceptive drum 10 to be sequentially separated from the photoreceptive drum 10 with a predetermined gap. A deceleration gear 31 which is a two-step gear is connected to a pinion gear 30 of a development unit driving motor (not shown). The deceleration gear 31 is connected to developing roller gears 20-K, 20-Y, 20-M, and 20-C via idle gears 32, 33, 34, and 35 and electronic clutches 36. The electronic clutches 36 are provided to correspond to the respective developing rollers 13a. The idle gears 32, 33, 34, and 35 are arranged in an appropriate number between the deceleration gear 31 and the electronic clutch 36 to transfer a rotational force of the gear 30 of the development unit driving motor to each of the electronic clutches 36. A first gear 37 connected to the idle gear 32 or 35 and a second gear 38 connected to the developing roller gear 20 are provided at opposite ends of each of the electronic clutches 36, as shown in FIG. 3. When the electronic clutch 36 is turned on, the rotation of the first gear 37 is transferred to the second gear 38 and the developing roller gear 20. When the electronic clutch 36 is turned off, the first gear 37 and the second gear 38 are disconnected.
In the operation of the driving apparatus of the development apparatus having the above structure, when the black developer 13-K is to be used, the development unit driving motor and the gear 30 are rotated clockwise. According to the rotation of the development unit driving gear 30, the first gears 37-K and 37-Y of the electronic clutches 36-K and 36-Y connected to the first idle gear 32 and the first gears 37-M and 37-C of the electronic clutches 36-M and 36-C connected to the second, third, and fourth idle gears 33, 34, and 35 are rotated. Next, when the electronic clutch 36-K for the black developer 13-K is turned on, the rotation of the first gear 37-K is transferred to the second gear 38-K. Accordingly, the developing roller gear 20-K and the developing roller 13a-K are driven. Here, a development bias voltage is applied to the developing roller 13a-K so that toner on the surface of the developing roller 13a-K develops the electrostatic latent image of the photoreceptive drum 10.
Next, to drive the yellow developing roller 13-Y, the development bias voltage applied to the black developing roller 13-K is cut off and the electronic clutch 36-K is turned off. Then, a development bias voltage for yellow is applied to the yellow developing roller 13-Y and the electronic clutch 36-Y is turned on, so that the rotation power of the first gear 37-Y is transferred to the second gear 38-Y. Thus, the developing roller gear 20-Y and the developing roller 13a-Y are driven. The development of magenta and cyan are sequentially performed in a similar manner.
However, since the driving apparatus of the developers having the above structure requires a plurality of electronic clutches, a cost for material increases.
To solve the above and/or other problems, the present invention provides a developer driving apparatus of a color image forming apparatus which sequentially drives developers by a mechanical means instead of an electronic clutch.
Additional aspects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.
According to an aspect of the present invention, a developer driving apparatus of a color image forming apparatus sequentially drives a plurality of developers for developing an electrostatic latent image formed on a photoreceptor body into predetermined colors. The developer driving apparatus comprises a reversible development unit driving motor which drives a developing roller of the developer, a deceleration gear which is rotated by being engaged with a gear of the development unit driving motor to provide a reduced angular velocity, a plurality of one-way gears which selectively receive a rotational driving force from the deceleration gear and rotate the corresponding developing roller according to a direction of rotation of the deceleration gear. Swing gears are adapted to selectively provide the driving force to the one-way gears by pivoting between the one-way gears. A swing drive gear supports and rotates the swing gear along a circumference of the swing drive gear. A swing arm pivotable about a shaft of the swing drive gear and having a first end connected to a shaft of the swing gear and a second end connected to a pivot unit positions the swing gear for engagement along a circumference of the swing drive gear. The swing arm and the pivot unit enable the swing gear to pivot between the pair of one-way gears according to a state of the pivot unit.
The swing gear pivot unit may comprise a plunger connected to the second end of the swing arm, and a solenoid into which the plunger is retracted and from which the plunger is partially ejected. The swing gear pivot unit may further comprise a spring which provides an elastic force to return the plunger to an original position when the solenoid is turned off. The spring may be positioned between the second end of the swing arm and the solenoid.
As the plunger is retracted into the solenoid when the solenoid is turned on, the swing arm pivots the swing gear from engagement with one of the pair of the one-way gears to engagement with the other of the pair of the one-way gears.
Each one-way gear comprises a first gear engaged with a respective swing gear, a second gear engaged with a respective developing roller gear, and a hub clutch arranged between the first and second gears to transfer a rotation force of the first gear to the second gear only when the first gear is rotated in one direction.
Idle gears are arranged in an odd number between the gear of the development unit driving motor and the swing drive gears to make the direction of rotation of the swing drive gears to be opposite.
The developer to be operated is determined according to the rotating direction of the development unit driving motor and the operation of the pivot unit.